PLANT DISEASE IN HYDROPONIC SYSTEMS
NFT, DFT, BAG CULTURES AND ROCKWOOL
Diseases occurring in hydroponic systems in NZ.
Root disease occurs in all types of hydroponic systems including NFT, and pumice and sawdust bag
culture, and in rockwool. The general perception is that there is less disease in hydroponic systems
using solid media (pumice, sawdust, rockwool or foam), and especially when the nutrient solution is
not recirculated, and that the disease incidence is greater in systems with recirculation such as NFT.
This general perception may not be correct.
Root diseases are very apparent in solution culture systems (NFT and deep flow systems) as the
roots can be seen and disease development on the roots is often noticed before there any symptoms
visible in the tops of the plants. Roots in bag cultures of pumice or sawdust are not usually examined
unless poor growth in the tops is apparent.
As consultants we submit many more root specimens for laboratory disease diagnosis from NFT
systems than we do from bag systems, but again this difference is probably as due more to the
visibility of disease than to the true incidence of disease.
Root disease is rarely due to a single pathogen, on average nearly three different disease organisms
are identified in every plant sample submitted for diagnosis. In the major greenhouse food crops
(tomatoes, peppers, cucumbers and lettuce) Pythium species are the commonest pathogen being
present in 81% of all specimens. Various species of Fusarium are the next commonest pathogens and
present in about 48% of specimens. Colletotrichum species ( which cause black dot on tomato
roots) are present in about 42% of specimens taken from NFT systems, and relatively rare in
specimens from pumice or sawdust. Corky root of tomatoes (caused by Pyrenchaeta lycopersici) has
only been found in specimens from pumice and sawdust and does not appear to occur in NFT
systems. Similarly we have not seen cucumber black root rot (caused by Phomopsis sclerotiodes) in
NFT systems but only in bag growing systems. Phytophthora species (mainly P.cryptogea strains) can
be extremely damaging in both NFT and bag culture, but is less common, occurring only about 27%
of specimens. Stem bacteriosis (often caused by Plectrosphaerella cucumerinum) is found in about
16%, and Rhizoctonia in about 14% of specimens. Bacterial diseases, affecting stems and leaves can
be transmitted via nutrient solutions, but laboratory diagnosis is often not needed, and hence have not
been considered in relation to the incidence of root disease.
Loss of roots and impairment of root function affects both water
relations and nutrient uptake by the host. Fungi may also affect
the host by producing toxins. Toxins produced within the roots
(either by the fungus or as a result of altered root metabolism)
typically result in vascular staining of the stems close to the
ground. Reduced water uptake and resultant hard growth and
wilting of the host and may induce water related physiological
diseases (e.g. blossom end rot of tomatoes , tip burn of
lettuce). Reduced nutrient uptake (calcium, magnesium and iron)
may sometimes affect leaf colour or result in obvious deficiency
Development of microflora in hydroponic systems
Hydroponic systems are not sterile environments in which the plant roots grow. Both solid media
systems (e.g.. rockwool and bag cultures) and liquid systems, such as NFT, rapidly develop a rich
microflora after planting the crops, even though the media may initially be sterile and free from
micro-organisms. The micro-organism present include fungi and bacteria and sometimes insects,
nematodes and arthropods. Organisms present within this microflora may feed on plant root
exudates, algae and dead plant material shed from the crop roots(saprophytes), other organism may
be predators or parasites of organisms found within the microflora and some bacteria in the microflora
may derive their energy from inorganic iron, manganese or sulphur compounds. Some members of
the microflora may be vectors of disease. This microflora may include organisms which are strict
pathogens (that is can only live as pathogens on live plant material) and will include many facultative
pathogens that can exist as either saprophytes or pathogens, but the pathogens are normally greatly
outnumbered by the non pathogenic microflora. The pathogen population can therefore be quite
limited by competition for food sources and by predation and parasitism by other members of a rich
microflora. The composition of the microflora will be affected by its environment, and hence the
microflora of an NFT system and a bag culture will be different. Bag cultures, which are well aerated
and nutrient rich and which provide large surface areas for colonisation by the microflora may well
provide more competition for pathogens than liquid cultures such as NFT.
Pythium, Phytophthora, Fusarium, and Rhizoctonia species are all facultative pathogens able to exist
well as saprophytes, and all of these organism can often be found in hydroponic systems where there
is no evidence of plant injury.
The natural microflora of hydroponic systems can develop very rapidly. Bacterial populations were
found to increase rapidly in a rockwool system with recirculating nutrient solution over the first 20
hours after planting with the population then remaining approximately constant at between 100,000
and 1 million bacteria per ml of solution for the following 12 weeks, while solution circulated
through rockwool slabs without plants contained only 500 -900 bacteria/ml (1). Microbial and
Pythium populations were shown to increase steadily as tomato plants grew in rockwool with and
without nutrient solution recirculation and in NFT systems over 180 days, but the Pythium
population was less and the severity of Pythium induced root rot was less in the closed (recirculating)
systems than in the run to waste systems (2). This was believed to be due to greater substrate
accumulation and higher competing microbial populations in the recirculated solution. More rapid
Phytophthora and Pythium root disease development in cucumbers and tomatoes in run to waste
systems than in recirculated systems has also been reported (11).
Interactions between disease organisms, hosts and environment
The number of NFT and bag crops severely affected by root rotting diseases is only a small
proportion of all the crops grown hydroponically in spite of the ability of the fungi concerned to
be extremely damaging in NFT systems. In many instances there may be many apparently
healthy plants within a crop where random individual plants are showing severe root disease
symptoms. Pythium has been consistently isolated from healthy lettuce root systems as well as
from lettuce with diseased roots in experimental work with NFT (3). Pythium was also isolated
consistently by baiting tests and isolations from NFT solutions on a commercial strawberry crop
which was healthy (4). It has been suggested that the development of epidemics of Phytophthora
root rot in tomatoes in NFT is the result of a complex interaction between root growth and
pathogen development (5).
The development of root disease in hydroponic systems may be due not only to introduction of
the causal fungi into the system but also to the condition of the crop and the nutrient solution.
Funck-Jensen and Hockenhull(3) have suggested that Pythium spp. can exist in NFT as
saprophytes, and that their growth(as saprophyte or parasites) is dependent on food supply (
substrate availability). The substrate is the combination of root exudates and breakdown products
of dead root tissue. Competition from other micro-organism in the NFT system for substrate must
also affect the growth of the pathogens. Adding sucrose to the NFT solution provided Pythium
with an alternate food source and resulted in much greater root death (3). Natural die back of
tomato roots (root death) which commonly occurs about the time of first harvests, may also
release large amounts of substrate for root rotting fungi and set off root disease. The abundance
of root exudates can be influenced by a number of factors including light intensity, temperature
and fruit load in crops such as tomatoes. Reduced substrate availability to the fungi may well
trigger increased oospore production.
The overall severity of root damage and effect on crop performance may well be the result of the
balance between rate of root attack by the fungi versus rate of new root growth. Tomatoes in
rockwool blocks maintained at 15° died following inoculation with Phytophthora, while similar
plants with rockwool kept at 25° remained symptomless although the fungus could detected on
their roots (6). Root growth rate is highly dependent on the supply of assimilates from the leaves
to the roots, and this can be reduced by heavy fruit load, deleafing, poor light or other growth
Bacterial canker of tomatoes (caused by Clavibacter michaganensis) has been shown to be
transmissible through NFT solutions (7), although in our experience the primary spread in tomatoes
in NZ is not through the solution. Recent work has shown that the population of canker bacteria in
NFT solution, and the incidence of the disease was much lower when the solution was kept at pH 5.0
than at pH 6.0, and that the survival lifetime of the bacteria in NFT solution was very short at low pH
The environment surrounding the root affects both the pathogen and host plant, and conditions
unfavourable to the host (such as low root temperatures) may favour the pathogen. Any check to
plant growth, or physical damage to the roots can weaken the host and increase susceptibility to
disease. Checks can be due to a fruit overload and lack of sufficient assimilate to maintain root health,
especially in dull weather, due to cold conditions, or sudden exposure of the roots to very high or
very low CF or pH.
Sources of disease infection
Undoubtedly the most common source of disease is the planting of infected disease carrying (but
often symptom free) plants into hydroponics systems. Pythium infections were found in from 1 to
76% of symptomless lettuce plants from two commercial nurseries in Belgium(9). Most transplants
used in hydroponic systems in NZ are propagated in peat or bark based composts, which are not
generally sterilised before use, and carry some risk of pathogen infestation. Peat and coir are not
uncommonly infected by Pythium, while bark is frequently claimed to have some fungistatic
properties. The infection risk depends very much on how hygienically potting composts are handled
during preparation and use. Steam sterilisation of peat and bark is not desirable because of increased
toxicity risks, methyl bromide sterilisation is safe and effective but its use will be prohibited soon.
Rockwool should be nearly sterile when delivered, and the disease risks of new pumice and sawdust
for bag filling should be very low provided that they are hygienically handled. Infected water sources
and greenhouse flooding by surface water is very common cause of disease, as is carry over of disease
within the greenhouse, on the hydroponic system, or on the floor or in the soil. Disease risks are quite
high with water taken from rivers, streams and shallow bores. Even water collected from greenhouse
roofs was found to infected with the tomato crown and root rot fungus (Fusarium oxysporum f.sp.
radicis lycopersici) in Holland (10).
Pythium, Phytophthora and Fusarium species can be brought into hydroponic systems by sciarids and
shore flies. The spread of disease in hydroponic systems is not limited to root fungal pathogens but
includes virus which can be introduced to the tops of the crop plants by many means including insect
vectors, but which can then be carried via the nutrient solution to infect other plants through their
roots. Cucumber green mottle virus is an outstanding and long recognised example of such
Spread of disease within hydroponic systems
Not all of the root diseases occurring in hydroponic systems are readily dispersed or transported by
recirculating nutrient solutions, but those fungi that are well adapted to living in water provide the
most severe disease problems. Pythium, Phytophthora and Rhizoctonia species are often referred to as
water moulds as they are particularly well adapted to water borne dispersal with the first two having
motile (swimming) zoospores as well as other spores and fruiting bodies that can be carried by water.
The corky root fungus ( Pyrenochaeta lycopersici ) is not spread in NFT solutions, but Didymella
lycopersici can be spread in NFT solutions, although such spread does not normally result in stem
lesions (7). Most diseases caused by Fusarium species, and by some Verticilium species, and black
dot disease of tomato roots (Colletotrichum sp.) appear to spread well through nutrient solutions, as
do many bacterial and virus diseases. Nematodes are not general a problem in hydroponically grown
food crops in NZ, but are readily spread in recirculating nutrient solutions.
DISEASE MANAGEMENT IN HYDROPONIC SYSTEMS
Disease management can be approached from two distinct directions, the first attempts to completely
eliminate any disease organisms from the hydroponic system, and the second approach is to limit the
crop loss from disease by a variety of methods. The first approach might be futile given the
practically impossible task of maintaining completely sterile conditions in large scale greenhouses, and
it seems that the best approach is one that manages disease incidence and disease effects on
Root disease management plans must use consider the following:
1. It is essential that only clean disease free water is used. Water samples can be tested for the
presence of pathogens by plant pathology laboratories. The water should be treated if
pathogens are found, but a failure to find pathogens in any one sample cannot be taken as
evidence that the water supply is disease free. All water from greenhouse roofs, dams,
springs, rivers, and shallow bores should be treated and only water from deep bores should
be considered as pathogen free.
2. It is essential that only disease free planting material is used.
3. Good hygiene and control of vectors such as sciarids and shore flies is essential.
4. Sterilisation of recirculating nutrient solutions. The Europeans are very strong advocates of some
form of sterilisation of recirculated nutrient solutions, especially for crops in rockwool and
pumice. However, there are still some European growers who recirculate nutrients solution
without any form of sterilisation treatment, and the usual philosophy is that sterilisation
treatments are a form of insurance to reduce the risk of disease spread through recirculated
5. Use biological controls. There is considerable research on microbiological antagonists of root
pathogens and the use of micro-organisms for cross protection against specific diseases.
Organisms used include a variety of bacteria and fungi including Pseudomonads, Fusarium
species and Trichoderma species. There are a number of commercially available products
containing Trichoderma. While encouraging results have been obtained in some instances, no
practical control methods giving complete control have so far emerged.
6. Root growth promoters are commercially available. There are a variety of products with claims for
improving weak root growth, including inorganic materials and organic material reputedly
containing hormones and other growth promoters ( including seaweed extracts), but few if
any of these products have been subjected to any rigorous scientific testing. Never the less
some growers have obtained good results from some of these products.
7. Fungicide incorporation in nutrient solutions. Treatments of recirculating systems with chemical
fungicides is sometimes recommended, more commonly for ornamental crops than food
crops, but few chemicals have specific activities against pathogens without harming the
Practical considerations affect the location of disinfection in hydroponic systems and the location can
affect the efficiency of disinfection methods. Disinfection methods are easier to apply to solutions
recirculated from hydroponic systems using solid media (rockwool, pumice, scoria, sawdust etc.) than
to solution cultures (NFT and deep flow systems) because of the relatively small volumes recycled
from solid media and the huge volumes circulating daily in solution cultures.
Figure 1 above shows a typical bag culture system. The large tank at left holds nutrient solution which
is pumped to the crop and delivered to the plants through a drip line. The run off from the pots is
collected by a gully and returned to sump tank on the right, from whence it is pumped bag into the
solution tank and mixed with fresh water (fw). If a solution treatment device is installed at position 1,
only the relatively small volume of run off solution is treated, the fresh water is not treated. If the
treatment device is installed at position 2, both the run off and fresh water is treated before it is
delivered to the crop. If a plant in only one bag is diseased then the run off water will be
contaminated, but only clean water will be delivered through the drip line to the other plants.
However, if the roots extend through the bottom of the bags into the collection gully then all plants
down stream of the diseased plant will be exposed to the disease, but the spread of disease will be
limited to plants in the same gully as the diseased plant. The spread of disease can only be prevented
by the treatment system if the plant roots are not in contact with the solution in the gully.
In an NFT system, the solution is held in the large sump tank and pumped to the top of the gullies,
flows over the plant roots and returns to the sump for recirculation. Fresh water is added directly to
the sump. If the treatment device is installed in position 1 then huge volumes of solution have to be
treated, but since root contact with the solution is unavoidable disease spread can only be limited to
the gully in which it first occurs. The difficulties and costs of treating huge volumes of solution have
led to the use of the treatment device at position 2. In this case a small proportion of the recirculating
solution is treated and returned directly to the sump. The total volume treated each day is several
times the volume contained within the system, and should greatly reduce the microbial and pathogen
population of the recirculating system but will not necessarily completely remove all pathogens from
the solution delivered to the top of the gullies.
Water and solution disinfection methods
Most disinfection methods act equally on the pathogens and on the competing microflora and
beneficial organism in the solution. Sterilisation methods using ozone, ultra violet light or heat are
completely non selective and kill all life forms at high doses.
Heat sterilisation is accomplished by passing the solution through a plate heat exchanger where the
solution is kept at 97° for 10 seconds. A second plate heat exchanger is used to cool the solution and
recover heat to improve the efficiency of the process. The process kills all bacteria, fungi and bacteria
(12). Unfortunately the process is very expensive to operate and uses 1 m3 of natural gas for heating
each m3 of drainwater sterilised. More recently it has been found easier to use a lower temperature of
85° for 30 seconds, as this allows the hot water required to be drawn from the normal hot water
boilers used for greenhouse heating. Heat sterilisation of nutrient solution has the highest operating
cost of any treatment method, but is the most effective.
Ultra violet radiation can be used for treating nutrient solution. Ultra violet radiation (light with a
wavelength of 254 nanometers) damages cellular nucleic acids in all living organisms, and organisms
receiving a large enough dose of UV radiation are killed. Water treatment by UV is achieved by
shining light from either low or high pressure UV lamps through a thin layer of flowing solution. The
solution must be clean and clear or light penetration through the solution is limited. The effectiveness
in killing micro-organisms depends on entirely on the dose given, and the dose required to kill varies
for each species. In general bacterial are killed readily at relatively low doses, pathogenic fungi require
higher doses, and different parts of any fungus may have different lethal doses, so that spores might
be killed more easily than pieces of mycellium; the highest doses are required to kill viruses(13). A
recent practical recommendation is that 100 mJ/cm2 should be used to treat recirculating solution for
fungal pathogen control or 250 mJ/cm2 for virus control (14).
It is very important that the best UV treatment equipment be installed and operated within the
manufacturers specifications if the proper dose is to be obtained. Practical requirements include
prefiltering the treated water to obtain best light transmission and using the correct water flow rate as
either too low or too high a flow rate will reduce the efficiency. UV water treatment equipment is
usually specified in term of light intensity (mW/cm2) and the dose is then the intensity multiplied by
the exposure time (expressed either as mW.seconds/cm2 or as mJ/cm2).
Complete treatment of all the drainage water in solid systems is quite feasible with UV, but with NFT
systems only partial treatment is feasible. A number of clients have used UV in this way for NFT
systems, resulting in reduced root disease, but not completely preventing root disease in all cases. UV
treatment completely eliminated Pythium from the solution in an experimental NFT lettuce system,
but accidentally introduced Pythium was not controlled (15). In another experiment with NFT lettuce
UV sterilisation treatment did not result in complete sterilisation but did result in 4 consecutive lettuce
crops without disease (16).
Ozone (O3) is a very powerful oxidising agent, and treatment of water or nutrient solutions with
ozone can result in the elimination of bacterial and fungal pathogens and viruses. Disease control is
complete if the redox potential of the treated solution is increased to 750 mV. In commercial
installations in Holland this required treatment of 1 m3 of drainwater with 10 g ozone for one hour.
The reliability of redox potential as a guide to zone concentration may be questionable, but it is a
simple and effective measurement (17 and 18) using relatively low cost redox meters. Effective ozone
treatment is not easy. Ozone treatment systems available in NZ use a venturi installed in pipe
through which there is a steady flow of solution to draw air through a an ozone generator. Some of
the oxygen in the air flowing through the generator is converted to ozone , and the ozone enriched
air is discharged as a stream of bubbles into the solution flowing through the venturi. The ozone has
to dissolve into the solution from these bubbles, and the contact time for solution is critical. The
discharge needs to pass into a deep solution tank or an absorption tower for maximum efficiency.
Much of the oxidising effect of the ozone is spent on organic matter and other materials in the
solution, and when solutions contain many reducing agents it is difficult to achieve a high redox
potential. The efficiency of ozonation can be increased very considerably by lowering the treated
solution to pH 4.0 by adding nitric acid before treatment (17). Ozone treatment systems must be
installed in a way that avoids ozone air pollution as ozone is dangerous to human and plant health.
Some clients, and particularly clients growing lettuce in NFT systems have installed ozone for partial
treatment of NFT solutions. Only in very few cases have growers been able to achieve high redox
potentials in the nutrient solutions, but in spite of this growers believe that disease incidence is
reduced. Lettuce growers also, and probably wrongly, believe that ozone is carried over in the
solution flowing down the gullies, but ozone has a very short half life, and this effect seems unlikely.
Other effects of UV and Ozone. Both UV treatment and Ozone breakdown some of the iron chelate in the solution and may cause
some precipitation of manganese compounds(19). They also breakdown many complex organic
compounds including insecticides and fungicides in nutrient solutions. Some insecticide and fungicide
breakdown products can be extremely phytotoxic. Ozone can be quite damaging to some plastic
components of NFT systems.
Slow Sand Filtration Slow sand filtration is being rapidly developed as a means of treating drainage water from hydroponic
systems. In the original systems the drainage water percolated through a deep bed (800-1200 mm) of
very fine filter sand (O-2 mm particles with an effective median diameter between 0.15 and 0.3 mm).
A flow rate of 100-300 litres per hour per m2 of sand bed surface area was achieved when the water
depth above the sand was about 800 mm.
Early filters were effective in controlling bacteria, Pythium and Phytophthora, but less effective for
Fusarium (13). Continuing research has shown that slightly coarser sand and other media can be
used, and that special rockwool granules may be the most efficient filter medium. The effectiveness of
slow sand filtration was originally believed to be due to the build up of particular microflora within
the filter bed, but it is now believed that both biological and mechanical filtration effects are involved.
Slow sand filters become more efficient after they have aged for some time. Some research workers
believe that slow sand filtration will reduce bacteria, fungi and viruses, but others found Fusarium and
tomato mosaic virus in the effluent from slow sand filters (20-23).
Disinfection by chemical dosing. Chlorination is a very old method of disinfecting water, but it is
usually recognised that doses effective in eliminating fungal pathogens are phytotoxic to greenhouse
crops, although it has been recommended as a treatment for fresh water in Australia (18). Hydrogen
peroxide has also been suggested for treatment of raw water and nutrient solutions. Hydrogen
peroxide is a much weaker oxidising agent than ozone, and relatively large amounts of hydrogen
peroxide have to be used (100 ppm for 5 minutes to kill condia of Fusarium oxysporum f.sp
lycopersici) and these rates are phytotoxic to crops,, but research is still in progress (24).
Disinfection methods for raw water It is vital that the raw water used for hydroponics is free from pathogens. All
surface water roof water and water from shallow bores or bores know to be contaminated with
pathogens should be treated. Water from reverse osmosis plants and water treated by membrane
filtration will be free from fungal and bacterial pathogens. Water treatment by UV and ozone is
relatively simply, if water in the holding tank is continuous treated by recirculation into the tank (see
our Client Note on water treatment). Continuous treatment overcomes much of the stringency of
dose rates needed for solution treatment.
Fungicide treatments applied to nutrient solutions.
In many countries overseas fungicide treatments of nutrient solution used for food crops are illegal,
and while not illegal in NZ, safety is somewhat questionable. The effectiveness of most fungicides is
also very limited, particularly as primary pathogens and especially Pythium readily mutate and become
resistant to repeated applications of the same fungicide. There is also considerable variation in
susceptibility to specific fungicides between different species of Pythium, and the usual diagnoses do
not identify Pythium species.
Treatment with biological competitors and control agents.
A number of commercial products are offered for this purpose but there has been little research to
prove their efficacy. Trichoderma species are widely mentioned in the literature and can readily
survive in NFT solutions and in solid media. Many bacteria with disease suppressing properties have
also been shown to be capable to forming stable populations in both nutrient solutions and on
At present there is no definite solution to the problems of plant disease in hydroponic systems. What
is clear however is that planting infected plant material and using infected water sources must be
avoided, and that root contact with drainage water in bag and other solid systems should be avoided.
Recirculation probably generates greater population of competing and controlling microbes than run
to waste systems, even though the risk of disease spread by recirculation is higher. Practical
applications of disinfection systems cannot guarantee freedom from disease, and are expensive, either
in capital or operating costs. The major risk of disease introduction to the crop from sources outside
the crop is always present, whether or not the recirculating solutions are disinfected. When the
solution is disinfected there may be less microbial buffering against disease, than when the solutions
have not been disinfected. Good hygiene in the greenhouse and in the surrounds remains imperative.
Good crop management to provide steady growth, without stress is probably a vital factor in
avoiding disease. Enrichment of the natural microflora with known disease antagonists such as
Trichoderma may be helpful.
1) Berklmann,B., Wohanka,W., and G.A. Wolf (1994) Characterisation of the bacterial flora in circulating nutrient
solutions of hydroponic system with rockwool. Acta Horticulturae 361:372-381.
2) Tu,J.C., Papadopoulos,A.P., Hao,X. and J.Zheng. (1999) The relationship of Pythium root rot and rhizosphere
micro-organisms in a closed circulating and open system in rockwool culture of tomato. Acta Horticulturae
3) Finck-Jensen,D and J.Hockenhull.(1983) The influence of some factors on the severity of Pythium
root rot of lettuce in soilless (hydroponic) growing systems. Acta Horticulturae 133:129-136 .
4) Price,T.V and P.D.Nolan.(1984) Incidence and distribution of Pythium, Phytophthora and Fusarium
sp.. in recirculating nutrient film hydroponic systems. ISOSC Proceedings 1984:523-529.
5) Pegg G.F and M.Holderness.(1984) Infection and disease development in NFT-grown tomatoes.
ISOSC Proceedings 1984:493-507.
6) Kennedy,R and G.F.Pegg.(1989) The effect of root zone temperature on the control of Phytophthora
cryptogea in rockwool-grown tomato plants. Acta Horticulturae 238,165-171 .
7) Staunton, W.P. and T.P.Cormican.(1978) The behaviour of tomato pathogens in a hydroponic system.
Acta Horticulturae 82: 133-135.
8) Huang,R. and J.C. Tu. (1999). Effect of the NFT solution pH on root transmission of tomato bacterial
canker (Clavibacter michiganensis subsp.. michaganensis). Acta Horticulturae 481: 569-575.
9)Vanachter,A. (1995) Development of Oplidium and Pythium in the nutrient solutions of NFT grown lettuce
and possible control methods. Acta Horticulturae 382:187-196.
10) Rattink,H. (1991) Epidemiology of Fusarium crown and root rot in artificial substrate systems.
Med.Fac.Landbouww. Rijksuniv.Gent,56/2b,423-30 (quoted by Runia 1994).
11) McPherson,G.M., Harriman,M.r., and D.Pattison. (1995). The potential for the spread of root diseases in
recirculating hydroponic systems and their control with disinfection. Med.Fac. Landbouwkundige en
Toegepaste Biologische,Wetenschappen,Univ.Gent 60(2b):317-379.
12) van Os,E.A., van de Braak,N.J., and G.Klomp. (1988). Heat treatment for disinfecting drainwater,
technical and economic aspects. Intnl Soc. Soilless Culture Proc. 1988: 353-359.
13) Wohanka,W. (1992) Slow sand filtration and UV radiation: low cost techniques for disinfection of
recirculating nutrient solution or surface water. Intnl Soc. Soilless Culture Proc. 1992:497-511.
14)Runia,W.Th. (1994). Elimination of root infecting pathogens in recirculation water from closed cultivation
systems by ultra violet radiation. Acta Horticulturae 361:361-371
15) Jamart.G., Bakyoni, J., and O. Kamouen. (1994). UV disinfection of recirculating nutrient solution in
closed horticulture systems. Med.Fac. Landbouwkundige en Toegepaste Biologische,
Wetenschappen,Univ.Gent 59(3a) 1071-1078.
16) Vanachter,A. (1995). Development of Oplidium and Pythium in nutrient solutions of NFT grown lettuce
and possible control methods. Acta Horticulturae 382: 187-196.
17) Runia, W.Th. (1994) Disinfection of water from closed cultivation systems with ozone. Acta Horticulturae
18) Mebalds,M., Bankier,M. and D. Beardsell. (1998) Disinfection of water for hydroponic systems. In Best of
Practical Hydroponics & Greenhouses, Casper Publications, Narabeen NSW, Australia: 126-132.
19) Acher,A,. Heuer,B., Rubinskaya,E and E.Fischer.(1997). Use of ultraviolet disinfected nutrient solutions
in greenhouses. J. Horticultural Science 72(1):117-123.
20) Wohanka,W. Disinfection of recirculating nutrient solutions by slow sand filtration. (1995). Acta
21) Wohanka,W. (1999) Optimisation of slow sand filtration as a means for disinfecting nutrient solutions.
Acta Horticulturae 481: 539-544.
22) van Os,A.E., van Kuik,F.J., Runia,W.Th., and J. van Buren. (1998) Prospects of slow sand filtration to
eliminate pathogens from recirculating solutions. Acta Horticulturae 458:377-382.
23) van Os,A.E., Amsing, J.J., van Kuik,A.J. and H. Willers. (1999). Slow sand filtration: A potential method
for the elimination of pathogens and nematodes in recirculating nutrient solutions from glasshouse grown
crops Acta Horticulturae 481:519-525.
24)Runia W.Th. (1995) A review of possibilities for disinfection of recirculation water from Soilless cultures.
Acta Horticulturae 382:221-229.
This client advice not replaces an earlier advice note “Root diseases in NFT systems” and supplements the
advice note “Hydroponics- Clean water”